Anaerobic Digestion of Pear Waste: Laboratory Equipment Design and Preliminary Results

Results of preliminary tests on the efficiency of the anaerobic contact process in reducing the pollution load of liquid pear processing waste indicated that the chemical oxygen demand (COD) of pear waste could be reduced by 75-95% depending on rate of addition of waste. Tests were made with 30 1 digesters (design and operation described in detail) using pear waste with COD concentrations of 13,000 to 120,000 ppm to which small amounts of ammonium and phosphate salts and yeast extract had been added to facilitate digestion. The reduction in COD was highest at long liquid retention times (10 to 86 days were tested) and was independent of the rate of addition of volatile (i.e. at 600°C) solids (0.8 to 2.2 kg/(m³) (day) [0.050.14 lb./(ft.³) (day)] were tested). Excess sludge solids (mainly undigestible pear waste particles) amounted to about 10% of the pear waste solids. Tests are being continued to determine optimum operating conditions.